Duplex smelting process.



A l E ANT , 'wooLsnv MCA. JoHNsoN AND mm w. HALE, or HARTFORD, CONNECTICUT, AssIGNo'as To THE CO I UOUS zINC FURNACE COMPANY, or HARTFORD,

' C0NNECTICUT,- a conroan ioN or. CCNNECT CUT.

No Drawing.

To all whom it may concern. 1

Be it known that we,WooLsnY MGA.

J oHNsoN' and EDWIN W. HALE, both citizens of the United States, and-both residing at Hartford, in the county of Hartford and State of Connecticut, have invented a newand- Improved Duplex Smelting Process, of

which the following-specification is a full disclosure. I 1-0 In its'fmore comprehensive aspect, this invention formulates a compound or multiphaseprocess for isolating volatile materials, notably such metals as zinc, from compounds thereof; and it utilizes the more economic portion of either .a special or'a conventional 'single-step'treatment as a primary-stage partial reduction and separation, and it then utilizes another treatment in the nature'of a secondary-stage operation for the extraction of the remnant values.

A primary object of this invention is to create a way, less costly than now known,

for deriving zinc from its oresby interrelating standard one-stage vexternally-fired zinc-retorting methods with electrical or-internally-heated smelting methods; and to do so in such a manner that the portions of each method displaying only the higher elficiency factors with relation to the composition of the charge during its course of treatment will be utilized harmoniously, While other less efficient portions will be dispensed Another object is to render available a system of oreftreatment in which one step will essentially be'carried out in an velectric furnace and which step will be preceded by certain steps conventional or otherwise, dealing with ores of a high zinccontent and which willextract those metallic values in- -volving a higher electric cost of recovery' and which will so condition the material as to bring it into the-state best'adapted for a high-efficiency in the electric furnace step.

This invbntion was evolved as a result ,of a duerecognition of certain fundamental facts heretofore not adequately grasped or interrelated by those skilled in this art, that is to say, the reduction of zinc.ores by dry methods has been commercially successful for a long time in the externally-fired or fuel-heated way, and we have in a semicommercial way established successfully the Specification of Letters Patent.- Patented D 21; 1915 Y Application filed March 16, 1914. Serial No; 825,190.

' tort process by first nprLEx s ELTING PROCESS.

ing two-thirds of the energy is expended.

The importance of this has hardly been appreciated or it has been regarded as a necessary evil; and its significanceand possibilities in relation to a characteristic of the electrical system was not grasped. This characteristic is that the electrical method attains its highest efliciency on mixtures such as may obtain in the retort during its low-efficiency end-period; e. 9. an electric zinc furnace operates less economically on [a 60% zinc charge which is comparatively costly to smelt electrically; although the last-third is cheaper and more effective than corresponding portions of other processes. The adaptability of this duplex process may perhaps be best illustrated by a typical practical application thereof. Assume a Joplin ore. of this composition:

(A). 90% Zns; 2% FeS 4% 10,, 1% A1 0,; 2% caco This is a high-grade zinc ore such as is conventionally treated for the ordinary reroasting to about this compositi on (B) 72 Zn; 1.5 Fe; 4.7 S102; 1.15 A120,; 3.03 CBLSO4.

Conventionally, also, this ore is then mixed with about 45% of its weight of coal and is introduced into cylindrical retorts and heated at temperatures progressively.

rising to 1350 C. or over, with a retort life o 6% Zn; s; s% Fe; $0,; 15% A1203; C and 5% CaS.

The percentage composition of (C) will depend upon the nature'of the reduction of about 30 days, and the commercially ex- 5 coal used and upon the nature of the ash thereof. e

: @20 tion permits the employment of a modified starting composition; 71. 0., one that conta ns .more iron" and lime ,and therefore which "Now, this process in such a case would modify this conventional complete treatment tallic v .j, .end-product which, instead of being con stituted like C,

changing it into an incomplete step which would yield a portion only of the mevalues, and which would result inan would be composed some what as follows: V I

(D) Zn; .5.% s; 18% 'SiO; C; Fe 6%,Al O 10%. y

First stage treatment.To do this, the ore (A) would be roasted tobring it into the composition (B) as before, but if desired higher in sulfur. Preferably'howeventhis roasted material will be -,mixed withxsome- 'what less .coal, say 25%, since the reduction ofthe metal isnot carried to a finality in .tlleyretorts; Or, instead of Working up to the aforesaid composition -(B), this invenwill tend to slag at a lower temperature than the convention composition B. This modification is made possible because this process f does not subject the starting composition. to temperatures as high as those needed in or- 1 b dinary retorting. Furthermore, retorts of greater capacity may'be employed with advantage, by reason of the moderate temperature of aboutll50? 0.; thereby keeping loss of zinc by volatilization lowdue tothe moderate temperature, and also avoiding the formation of slag in the retort or causing undue corrosion ofthe retorts. This also ef-.

fects areduction in the soakage loss by reason, of the decreased discarding of 'retorts due to their increased life; The moderate temperatures used and the fact that the charge is not forced, makes it feasible to use retorts 11 inches or 12 inches square, instead of 8-} round,,."and the charge (such as D) now analyzing say 20% zinc with about 30%. fixed carbon may easily be In ordinary reto-rting practice, a difficulty arises at the end of the operation in respect to determining what had best be the finishing temperature and in controlling the final heating so as not to exceed the practically estimated maximum. The reason for this lies in the endothermic character of the reaction This means that so long as this reaction is taking place, at asubstantial rate, the heat absorbed by the reaction is cooling the retort, and when this refrigerating effect abruptly ceases while yet the furnace is under full fire, then the retort contents will attain a'destructively high temperature before the operator can sufficiently check the furnace.

By our system, however,- there need be no CaO; 12% SiO 4% A1 0,; 13%

opportunity for this uncontrollable temperature uprise, because the heating is terminated considerably before the end of the endothermic reduction and the .operation does not need to hug thedanger point.

Secogid stage trca'tment.The second stage 'treatment will now be applied for the purpose of recovering the metallic values of the residue D, and the preliminary steps of this treatment are forthe purpose of preparing the charge for thefelectric furnace. Prefer-' 7 ably, this preparation follows the teachings of the Johnson U; S; Patent No. 868345, granted October 15,1907, in that the charge is made to containmetallic iron for the purpose of decomposing the zinc sulfid in the electric furnace, and it is .so constituted as to enablethe furnace to be operated in ac cordance with the Johnson Canadian Patent NO. 146134, granted February' 25, .1913.

' Thus, the residue D may be mixed with low grade ore analyzing green, say, 15% zinc, 10%- lead, 2% copper, 22% iron and 25% sulfur. This green ,ore will be first roasted to lower its sulfur content to adesired minimum by utilizing the relatively low roasting temperature of 850 to 900 centigrade, the

'efiect of which will be to convert the larger portions of the'sulfates of iron and zinc into oxids. -It is not necessary to dead-roast this bon, or by incorporating a certain amount of crude oil into charge. This facilitatesthe operation of the charge in the electric fur nace by aifording'a liberal diffusion of re ducing elements throughout the charge. This additional green ore having been first roasted to reduce thev sulfur to workable limits, its addition tothe retort residue D furnishes. the latter with the oxygen necessary to consume its excess of fixed carbon and prevent carbon from accumulating in the electric furnace. This mixture may be represented as followsz v r 30 Zn; 12 Fe; 1.575 011; 8 The iron oxidin this charge must now be converted into sponge iron to a large extent in the preheating forfmetallizing operation. Enough" carboli'pr' other reducing agent hadbeen brought into the. mixture as i abovedescribed in percentages sufliciently high to eifect this metallizing of the or less extent, or by such leaks as would happen in the ordinary course of events. This second heating or so-called preheating or metallizing is carried onv in a furnace of the mufiie type to a final temperature of about l000 Centigrade under reducing conditions. This preliminary preheating treatment yields a mixture in ac-.

cord-ance with the teachings of the above mentioned patents, and electric smelting of preheating charge is so carried on recovery high percentages of zinc, copper, gold, silver and lead in merchantable form. v

The composition D (yielded by the retort after the partial recovery of zinc) may be given slagging characteristics bymixing it with suitable 'retorted material, instead of with roasted green ore. That is to say,.two

difli'erent non-slagging mixtures, the one acidand the other basic, may be separately retorted either intermittently or continuously and they may thereafter be mixed together in such proportions and if needed with such other side material as will compound a true slagging mixture suitable for smelting in the electric furnace.

. Having thus revealed this invention, we claim as new and desire to secure by Letters Patent of the United States: I 1.,A smelting process of the'nature disclosed, consisting in preparing a self-reducing charge; inserting said charge within a suitable retort; externally heating said retort tor a sufiicient time-period to effect a partial reduction only of the contained charge, and discontinuing the external heating of the charge at a temperature materially short of that essential for a commercially ultimate reduction; and finally completingthe reduction to a coml'nercially-ultimate extent by means of materially higher temperatures obtained by suitably developing heat within the charge inclosed in a suitable container.

2. A smelting process of the nature disclosed, consisting in preparing a self-reducing mixture: bringing said mixture within a suitable retort; externally heating said retort for a suilicient time and at a sufficient temperature to effect an incomplete reduction of the mixture and obtain a partial re covery of the metallic value; and finally completing the reduction and effectinga commercially ultimate recovery of the metallie value by suitably developing internal heat within the partially treated mixture at temperatures materially higher than obtained by the external heating.

3. The process revealedfor producing a volatile metal consisting inpreparing a selfreducing charge containing a compound of -said metal; inserting said charge within a suitable retort; externally heating said retort to effect an incomplete reduction of the contained charge, withdrawing the volatilized reduced metal from said retort, and terminating the effective heating of the charge materially short of the point of ultimate commercial reductiongthereafter raising the pre-treated charge inclosed in a suit-able .c'ontainer to materially higher temperatures by internally applying heat thereto until the point of ultimate commercial reductiolf is attained, and meanwhile \vlthdrawing an recovering the volatilized metal. F

4. A process for reducing high-grade zinc ores consisting in obtaining the zinc-bearing material in a state having a-low sulfurcontent, then forming a retort charge thereof by the addition of carbon, then'heating said mixture in aretort externally heated to a temperature rising to about 1150 C., as a maximum, thereafter utilizing the residue from said retort together with additional carbon for preparing another mixture, and then obtaining the ultimate metallic values by electrically developing heat within the charge while inclosed in an air-excluding container.

5. A process of the nature revealed for extracting values from zinc ores, which consists in effecting a preliminary partial recovery of metallic zinc by first reducing the zinc-bearing material in externally heated fire-clay retorts under non-slagging conditions, and then applying electric heat under slagging conditions, thereby recovering the residual zinc and other values. 7 1

In witness whereof, we hereunto subscribe our names, as attested by the two subscribing witnesses. 

